Circulation in a fluid ejection device

ABSTRACT

A fluid ejection device may include a discharge port, an energy generating element to discharge liquid through the discharge port, a first liquid supply on a first side of the discharge port, a second liquid supply on a second side of the discharge port opposite the first side, a first liquid flow path extending from the first liquid supply to the discharge port, a second liquid flow path extending from the second liquid supply to the discharge port and a fluid displacement actuator in the first liquid flow path.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application claiming priorityunder 35 USC § 120 from co-pending U.S. patent application Ser. No.15/433,827 filed on Feb. 15, 2017 which is a continuation of U.S. patentapplication Ser. No. 15/252,433 filed on Aug. 31, 2016 and issued asU.S. Pat. No. 9,623,659 on Apr. 18, 2017, which is a continuation ofU.S. patent application Ser. No. 14/958,022 filed on Dec. 3, 2015 andissued as U.S. Pat. No. 9,457,584 on Oct. 4, 2016, which is acontinuation of U.S. patent application Ser. No. 14/241,330 filed onFeb. 26, 2014 and issued as U.S. Pat. No. 9,211,721 on Dec. 15, 2015,which is a national application filed under 37 CFR 371 and claimingparty from PCT/US2011/05361 filed on Sep. 28, 2011.

BACKGROUND

Fluid ejection devices in inkjet printers provide drop-on-demandejection of fluid drops. Inkjet printers produce images by ejecting inkdrops through a plurality of nozzles onto a print medium, such as asheet of paper. The nozzles are typically arranged in one or morearrays, such that properly sequenced ejection of ink drops from thenozzles causes characters or other images to be printed on the printmedium as the printhead and the print medium move relative to eachother. In a specific example, a thermal inkjet printhead ejects dropsfrom a nozzle by passing electrical current through a heating element togenerate heat and vaporize a small portion of the fluid within a firingchamber. Some of the fluid displaced by the vapor bubble is ejected fromthe nozzle. In another example, a piezoelectric inkjet printhead uses apiezoelectric material actuator to generate pressure pulses that forceink drops out of a nozzle.

Although inkjet printers provide high print quality at reasonable cost,their continued improvement depends in part on overcoming variousoperational challenges. For example, the release of air bubbles from theink during printing can cause problems such as ink flow blockage,insufficient pressure to eject drops, and mis-directed drops.Pigment-ink vehicle separation (PIVS) is another problem that can occurwhen using pigment-based inks. PIVS is typically a result of waterevaporation from ink in the nozzle area and pigment concentrationdepletion in ink near the nozzle area due to a higher affinity ofpigment to water. During periods of storage or non-use, pigmentparticles can also settle or crash out of the ink vehicle which canimpede or block ink flow to the firing chambers and nozzles in theprinthead. Other factors related to “decap”, such as evaporation ofwater or solvent can cause PIVS and viscous ink plug formation. Decap isthe amount of time inkjet nozzles can remain uncapped and exposed toambient environments without causing degradation in the ejected inkdrops. Effects of decap can alter drop trajectories, velocities, shapesand colors, all of which can negatively impact the print quality of aninkjet printer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 illustrates an inkjet printing system suitable for incorporatinga fluid ejection device for implementing slot-to-slot fluid circulationas disclosed herein, according to an embodiment;

FIGS. 2a and 2b show a top down view of a fluid ejection device,according to embodiments;

FIG. 3 shows a cross-sectional view of a fluid ejection device thatcorresponds generally with the top down view of FIGS. 2a and 2b ,according to an embodiment;

FIG. 4 shows a top down view of a fluid ejection device, according to anembodiment;

FIG. 5 shows a top down view of a fluid ejection device, according to anembodiment;

FIG. 6 shows a top down view of a fluid ejection device, according to anembodiment;

FIG. 7 shows a top down view of a fluid ejection device, according to anembodiment;

FIG. 8 shows a fluidic channel having closed fluid pump chambers withfluid pump actuators located toward each end of the channel, accordingto an embodiment;

FIG. 9 shows a fluidic channel having closed fluid pump chambers withpiezoelectric fluid pump actuators located toward each end of thechannel, according to an embodiment;

FIG. 10 shows a fluidic channel having closed fluid pump chambers withpiezoelectric fluid pump actuators located toward each end of thechannel, according to an embodiment;

FIG. 11 shows a flowchart of an example method of circulating fluid fromslot-to-slot in a fluid ejection device, according to an embodiment.

DETAILED DESCRIPTION

Overview of Problem and Solution

As noted above, various challenges have yet to be overcome in thedevelopment of inkjet printing systems. For example, inkjet printheadsused in such systems sometimes have problems with ink blockage and/orclogging. One cause of ink blockage is an excess of air that accumulatesas air bubbles in the printhead. When ink is exposed to air, such aswhile the ink is stored in an ink reservoir, additional air dissolvesinto the ink. The subsequent action of ejecting ink drops from thefiring chamber of the printhead releases excess air from the ink whichthen accumulates as air bubbles. The bubbles move from the firingchamber to other areas of the printhead where they can block the flow ofink to the printhead and within the printhead. Bubbles in the chamberabsorb pressure, reducing the force on the fluid pushed through thenozzle which reduces drop speed or prevents ejection.

Pigment-based inks can also cause ink blockage or clogging inprintheads. Inkjet printing systems use pigment-based inks and dye-basedinks, and while there are advantages and disadvantages with both typesof ink, pigment-based inks are generally preferred. In dye-based inksthe dye particles are dissolved in liquid so the ink tends to soakdeeper into the paper. This makes dye-based ink less efficient and itcan reduce the image quality as the ink bleeds at the edges of theimage. Pigment-based inks, by contrast, consist of an ink vehicle andhigh concentrations of insoluble pigment particles coated with adispersant that enables the particles to remain suspended in the inkvehicle. This helps pigment inks stay more on the surface of the paperrather than soaking into the paper. Pigment ink is therefore moreefficient than dye ink because less ink is needed to create the samecolor intensity in a printed image. Pigment inks also tend to be moredurable and permanent than dye inks as they smear less than dye inkswhen they encounter water.

One drawback with pigment-based inks, however, is that ink blockage canoccur in the inkjet printhead due to factors such as prolonged storageand other environmental extremes that can result in inadequateout-of-box performance of inkjet pens. Inkjet pens have a printheadaffixed at one end that is internally coupled to an ink supply. The inksupply may be self-contained within the printhead assembly or it mayreside on the printer outside the pen and be coupled to the printheadthrough the printhead assembly. Over long periods of storage,gravitational effects on the large pigment particles, randomfluctuations, and/or degradation of the dispersant can cause pigmentagglomeration, settling or crashing. The build-up of pigment particlesin one location can impede or block ink flow to the firing chambers andnozzles in the printhead, resulting in poor out-of-box performance bythe printhead and reduced image quality from the printer. Other factorssuch as evaporation of water and solvent from the ink can alsocontribute to PIVS and/or increased ink viscosity and viscous plugformation, which can decrease decap performance and prevent immediateprinting after periods of non-use.

Previous solutions have primarily involved servicing printheads beforeand after their use, as well as using various types of external pumpsfor circulating the ink through the printhead. For example, printheadsare typically capped during non-use to prevent nozzles from cloggingwith dried ink. Prior to their use, nozzles can also be primed byspitting ink through them or using the external pump to purge theprinthead with a continuous flow of ink. Drawbacks to these solutionsinclude a reduced ability to print immediately (i.e., on demand) due tothe servicing time, and an increase in the total cost of ownership dueto the consumption of ink during servicing. The use of external pumpsfor circulating ink through the printhead is typically cumbersome andexpensive, involving elaborate pressure regulators to maintainbackpressure at the nozzle entrance. Accordingly, decap performance,PIVS, the accumulation of air and particulates, and other causes of inkblockage and/or clogging in inkjet printing systems continue to befundamental issues that can degrade overall print quality and increaseownership costs, manufacturing costs, or both.

Embodiments of the present disclosure reduce ink blockage and/orclogging in inkjet printing systems generally by circulating fluidbetween fluid supply slots (i.e., from slot-to-slot). Fluid circulatesbetween the slots through fluidic channels that include pump chambershaving fluid displacement actuators to pump the fluid. The fluidactuators are located asymmetrically (i.e., off-center, oreccentrically) toward ends of the fluidic channels in chambers that areadjacent to respective fluid supply slots. The asymmetric location ofthe actuators toward the ends of the fluidic channels, along withasymmetric activation of the actuators to generate compressive andexpansive (tensile) fluid displacements of different durations, createsdirectional fluid flow through the channels from slot-to-slot. In someembodiments, the fluid actuators are controllable such that thedurations of forward (i.e., compressive) and reverse (i.e., expansive,or tensile) actuation/pump strokes can be controlled to vary thedirection of fluid flow through the channels.

In one embodiment, a fluid ejection device includes a die substratehaving first and second elongated fluid slots along opposite sides ofthe substrate and separated by a substrate central region. First andsecond internal columns of closed chambers are associated, respectively,with the first and second slots. The internal columns are separated bythe central region. Fluidic channels extend across the central region tofluidically couple closed chambers from the first internal column withclosed chambers from the second internal column. Pump actuators in eachclosed chamber pump fluid through the channels from slot to slot.

In one embodiment, a fluid ejection device includes first and secondfluid slots along opposite sides of a substrate. A first column of dropejection chambers is adjacent to the first slot toward the center of thesubstrate, and a second column of drop ejection chambers is adjacent tothe second slot toward the center of the substrate. Fluidic channelsextend across the center of the substrate, coupling the first and secondslots through drop ejection chambers in the first and second columns.Pump chambers are in the fluidic channels next to the drop ejectionchambers. The pump chambers have pump actuators to circulate fluidthrough the channels from slot to slot.

In one embodiment, a method of circulating fluid from slot-to-slot in afluid ejection device includes pumping fluid over a central area of adie substrate from a first slot to a second slot through a first fluidicchannel. The first fluidic channel extends from the first slot through afirst chamber adjacent the first slot, across the central area, and tothe second slot through a second chamber adjacent the second slot. Themethod includes pumping fluid over the central area from the second slotto the first slot through a second fluidic channel. The second fluidicchannel extends from the second slot through a third chamber adjacentthe second slot, across the central area, and to the first slot througha fourth chamber adjacent the first slot.

Illustrative Embodiments

FIG. 1 illustrates an inkjet printing system 100 suitable forincorporating a fluid ejection device for implementing slot-to-slotfluid circulation as disclosed herein, according to an embodiment of thedisclosure. Inkjet printing system 100 includes an inkjet printheadassembly 102, an ink supply assembly 104, a mounting assembly 106, amedia transport assembly 108, an electronic printer controller 110, andat least one power supply 112 that provides power to the variouselectrical components of inkjet printing system 100. Inkjet printheadassembly 102 includes at least one fluid ejection device 114 (printhead114) that ejects drops of ink through a plurality of orifices or nozzles116 toward a print medium 118 so as to print onto print media 118. Printmedia 118 can be any type of suitable sheet or roll material, such aspaper, card stock, transparencies, Mylar, and the like. Nozzles 116 aretypically arranged in one or more columns or arrays such that properlysequenced ejection of ink from nozzles 116 causes characters, symbols,and/or other graphics or images to be printed on print media 118 asinkjet printhead assembly 102 and print media 118 are moved relative toeach other.

Ink supply assembly 104 supplies fluid ink to printhead assembly 102from an ink storage reservoir 120 through an interface connection, suchas a supply tube. The reservoir 120 may be removed, replaced, and/orrefilled. In one embodiment, as shown in FIG. 1, ink supply assembly 104and inkjet printhead assembly 102 form a one-way ink delivery system. Ina one-way ink delivery system, substantially all of the ink supplied toinkjet printhead assembly 102 is consumed during printing. In anotherembodiment (not shown), ink supply assembly 104 and inkjet printheadassembly 102 form a recirculating ink delivery system. In arecirculating ink delivery system, only a portion of the ink supplied toprinthead assembly 102 is consumed during printing. Ink not consumedduring printing is returned to ink supply assembly 104.

Mounting assembly 106 positions inkjet printhead assembly 102 relativeto media transport assembly 108, and media transport assembly 108positions print media 118 relative to inkjet printhead assembly 102.Thus, a print zone 122 is defined adjacent to nozzles 116 in an areabetween inkjet printhead assembly 102 and print media 118. In oneembodiment, inkjet printhead assembly 102 is a scanning type printheadassembly. As such, mounting assembly 106 includes a carriage for movinginkjet printhead assembly 102 relative to media transport assembly 108to scan print media 118. In another embodiment, inkjet printheadassembly 102 is a non-scanning type printhead assembly. As such,mounting assembly 106 fixes inkjet printhead assembly 102 at aprescribed position relative to media transport assembly 108. Thus,media transport assembly 108 positions print media 118 relative toinkjet printhead assembly 102.

Electronic printer controller 110 typically includes components of astandard computing system such as a processor, memory, firmware,software, and other electronics for controlling the general functions ofsystem 100 and for communicating with and controlling system componentssuch as inkjet printhead assembly 102, mounting assembly 106, and mediatransport assembly 108. Electronic controller 110 receives data 124 froma host system, such as a computer, and temporarily stores data 124 in amemory. Typically, data 124 is sent to inkjet printing system 100 alongan electronic, infrared, optical, or other information transfer path.Data 124 represents, for example, a document and/or file to be printed.As such, data 124 forms a print job for inkjet printing system 100 andincludes one or more print job commands and/or command parameters.

In one embodiment, electronic printer controller 110 controls inkjetprinthead assembly 102 for ejection of ink drops from nozzles 116. Thus,electronic controller 110 defines a pattern of ejected ink drops whichform characters, symbols, and/or other graphics or images on print media118. The pattern of ejected ink drops is determined by the print jobcommands and/or command parameters. In one embodiment, electroniccontroller 110 includes fluid circulation module 126 stored in a memoryof controller 110. Fluid circulation module 126 executes on electroniccontroller 110 (i.e., a processor of controller 110) to control theoperation of one or more fluid actuators integrated as pump actuatorswithin fluid ejection device 114. More specifically, in one embodimentcontroller 110 executes instructions from fluid circulation module 126to control which pump actuators within fluid ejection device 114 areactive and which are not active. Controller 110 also controls the timingof activation for the pump actuators. In another embodiment, where thepump actuators are controllable, controller 110 executes instructionsfrom module 126 to control the timing and duration of forward andreverse pumping strokes (i.e., compressive and expansive/tensile fluiddisplacements, respectively) of the pump actuators in order to controlthe direction, rate, and timing of fluid flow through fluidic channelsbetween fluid feed slots within fluid ejection device 114.

In one embodiment, inkjet printhead assembly 102 includes one fluidejection device (printhead) 114. In another embodiment, inkjet printheadassembly 102 is a wide array or multi-head printhead assembly. In oneimplementation of a wide-array assembly, inkjet printhead assembly 102includes a carrier that carries fluid ejection devices 114, provideselectrical communication between fluid ejection devices 114 andelectronic controller 110, and provides fluidic communication betweenfluid ejection devices 114 and ink supply assembly 104.

In one embodiment, inkjet printing system 100 is a drop-on-demandthermal bubble inkjet printing system wherein the fluid ejection device114 is a thermal inkjet (TIJ) printhead. The thermal inkjet printheadimplements a thermal resistor ejection element in an ink chamber tovaporize ink and create bubbles that force ink or other fluid drops outof a nozzle 116. In another embodiment, inkjet printing system 100 is adrop-on-demand piezoelectric inkjet printing system wherein the fluidejection device 114 is a piezoelectric inkjet (PIJ) printhead thatimplements a piezoelectric material actuator as an ejection element togenerate pressure pulses that force ink drops out of a nozzle.

FIG. 2 (FIGS. 2a and 2b ) shows a top down view of a fluid ejectiondevice 114, according to an embodiment of the disclosure. FIG. 3 shows across-sectional view of a fluid ejection device 114 that correspondsgenerally with the top down view of FIG. 2a . Referring generally toFIGS. 2a and 3, fluid ejection device 114 includes a silicon diesubstrate 200 with a first fluid supply slot 202 and a second fluidsupply slot 204 formed therein. Fluid slots 202 and 204 are elongatedslots that are in fluid communication with a fluid supply (not shown),such as a fluid reservoir 120 (FIG. 1). While the concepts ofslot-to-slot fluid circulation are discussed throughout the disclosurewith respect to fluid ejection devices having two fluid slots, suchconcepts are not limited in their application to devices with two fluidslots. Rather, fluid devices having more than two fluid slots, such assix or eight slots, for example, are also contemplated as being suitabledevices for implementing slot-to-slot fluid circulation. In addition, inother embodiments the configuration of the fluid slots may vary. Forexample, the fluid slots in other embodiments may be of varying shapesand sizes such as round holes, square holes, square trenches, and so on.

Fluid ejection device 114 includes a chamber layer 206 having walls 208that define fluid chambers 210, 212, and that separate the substrate 200from a nozzle layer 214 having nozzles 116. Chamber layer 206 and nozzlelayer 214 can be formed, for example, of a durable and chemically inertpolymer such as polyimide or SU8. In some embodiments the nozzle layer214 may be formed of various types of metals including, for example,stainless steel, nickel, palladium, multi-layer structures of multiplemetals, and so on. Fluid chambers 210 and 212 comprise, respectively,fluid ejection chambers 210 and fluid pump chambers 212. Fluid chambers210 and 212 are in fluid communication with a fluid slot. Fluid ejectionchambers 210 have nozzles 116 through which fluid is ejected byactuation of a fluid displacement actuator 216 (i.e., a fluid ejectionactuator 216 a). Fluid pump chambers 212 are closed chambers in thatthey do not have nozzles through which fluid is ejected. Actuation offluid displacement actuators 216 (i.e., fluid pump actuators 216 b)within pump chambers 212 generates fluid flow between slot 202 and 204as discussed in greater detail below.

As is apparent from FIGS. 2a and 2b , chambers 210 and 212 form columnsof chambers along the inner and outer sides of slots 202 and 204. In theembodiments of FIGS. 2a and 2b , a first external column 218 a isadjacent to the first fluid slot 202 and located between the slot 202and an edge of the substrate 200. A second external column 218 b isadjacent to the second fluid slot 204 and located between the slot 204and another edge of the substrate 200. A first internal column 220 a ofchambers is adjacent to the first fluid slot 202 and located between theslot 202 and the center of the substrate 200. A second internal column220 b is adjacent to the second fluid slot 204 and located between theslot 204 and the center of the substrate 200. In the embodiment of FIGS.2a and 3, chambers in the external columns 218 are fluid ejectionchambers 210, while chambers in the internal columns 220 fluid pumpchambers 212. In other embodiments, however, the external and internalcolumns can include both fluid ejection chambers 210 and fluid pumpchambers 212. For example, the embodiment shown in FIG. 2b has internalcolumns 220 a and 220 b with both fluid ejection chambers 210 and fluidpump chamber 212. The FIG. 2b embodiment provides slot-to-slotrecirculation through channels 222 while only reducing the nozzleresolution of the internal columns 220 a and 220 b by half.

Fluid displacement actuators 216 are described generally throughout thedisclosure as being elements capable of displacing fluid in a fluidejection chamber 210 for the purpose of ejecting fluid drops through anozzle 116, and/or for generating fluid displacements in a fluid pumpchamber 212 for the purpose of creating fluid flow between slots 202 and204. One example of a fluid displacement actuator 216 is a thermalresistor element. A thermal resistor element is typically formed of anoxide layer on the surface of the substrate 200, and a thin film stackthat includes an oxide layer, a metal layer and a passivation layer(individual layers are not specifically illustrated). When activated,heat from the thermal resistor element vaporizes fluid in the chamber210, 212, causing a growing vapor bubble to displace fluid. Apiezoelectric element generally includes a piezoelectric materialadhered to a moveable membrane formed at the bottom of the chamber 210,212. When activated, the piezoelectric material causes deflection of themembrane into the chamber 210, 212, generating a pressure pulse thatdisplaces fluid. In addition to thermal resistive elements andpiezoelectric elements, other types of fluid displacement actuators 216may also be suitable for implementation in a fluid ejection device 114to generate slot-to-slot fluid circulation. For example, fluid ejectiondevices 114 may implement electrostatic (MEMS) actuators,mechanical/impact driven actuators, voice coil actuators,magneto-strictive drive actuators, and so on.

In one embodiment, as shown in FIGS. 2 and 3, a fluid ejection device114 includes fluidic channels 222. Fluidic channels 222 extend from thefirst fluid slot 202, across the center of the die substrate 200 and tothe second fluid slot 204. Therefore, fluidic channels 222 couple thefluid pump chambers 212 of the first internal column 220 a withrespective fluid pump chambers 212 of the second internal column 220 b.The fluid pump chambers 212 are in the fluidic channels 222 and can beconsidered to be part of the channels 222. Thus, each fluid pump chamber212 is located asymmetrically (i.e., off-centered, or eccentrically)within a fluidic channel 222, toward an end of the channel.

As shown in the legend boxes of FIGS. 2 and 3, some fluid pump actuators216 b in the internal columns 220 a and 220 b are active and some areinactive. Inactive pump actuators 216 b are designated with an “X”. Thepattern of active and inactive pump actuators 216 b is controlled bycontroller 110 executing fluid circulation module 126 (FIG. 1) togenerate fluid flow through channels 222 that circulates fluid betweenthe first slot 202 and the second slot 204. Direction arrows show whichdirection fluid flows through channels 222 between slots 202 and 204.The direction of fluid flow through a channel 222 is controlled byactivating one or the other of the fluid pump actuators 216 b at theends of the channel 222. Thus, various fluid circulation patterns can beestablished between slots 202 and 204 by controlling which pumpactuators 216 b are active and which are not active. As shown in theFIG. 2 example, controlling groups of pump actuators 216 b to be activeand inactive generates fluid flowing from the first slot 202 to thesecond slot 204 through some channels 222, and from the second slot 204back to the first slot 202 through other channels 222. Channels 222 inwhich no pump actuator 216 b is active have little or no fluid flow.

FIG. 4 shows a top down view of a fluid ejection device 114, accordingto an embodiment of the disclosure. The FIG. 4 embodiment is similar tothe embodiment described in FIGS. 2 and 3, except that an additionalfluidic channel enables further slot-to-slot fluid circulation aroundthe perimeter of the die substrate 200. A perimeter fluidic channel 400is disposed along both sides and both ends of the substrate 200. Theperimeter fluidic channel 400 is fluidically coupled to both fluidejection chambers 210 and fluid pump chambers 212 from the firstexternal column 218 a and the second external column 218 b. Thus, unlikethe embodiment described with reference to FIGS. 2 and 3, the external218 and internal 220 columns include both fluid ejection chambers 210and fluid pump chambers 212. Fluid circulation patterns are determinedin this embodiment based on the channels 222 in which fluid pumpchambers 212 (and pump actuators 216 b) are located, and based on wherefluid pump chambers 212 are located in the external columns 218. Thus,fluid circulation across the center of the die substrate 200 fromslot-to-slot will occur through channels 222 having fluid pump chambers212 but not through channels 222 without fluid pump chambers. Likewise,fluid circulation between slots 202 and 204 around the perimeter fluidicchannel 400 occurs through fluid pump chambers 212 in the externalcolumns 218. As in the previous embodiment, the fluid circulation module126 executing on controller 110 to control which pump actuators 216 bare active and inactive determines which direction the fluid circulatesbetween the slots through channels 222 and 400.

FIG. 5 shows a top down view of a fluid ejection device 114, accordingto an embodiment of the disclosure. The FIG. 5 embodiment is similar tothe embodiment described in FIGS. 2 and 3, except that both the externalcolumns 218 of chambers and the internal columns 220 of chambers havefluid ejection chambers 210 without any fluid pump chambers 212. In thisembodiment, instead of having fluid pump chambers 212 taking up chamberlocations around the fluid slots 202, 204, that could otherwise be usedfor fluid ejection chambers 210, additional chamber locations are formedfurther toward the center of the die substrate 200 within the channels222 that provide for fluid pump chambers 212 and associated pumpactuators 216 b. Thus, as shown in FIG. 5, pump actuators 216 b in fluidpump chambers 212 toward either end of a channel 222 can be activated bya controller 110 to generate fluid flow through the channel 222 ineither direction. Controlling groups of pump actuators 216 b to beactive and inactive generates fluid flowing from the first slot 202 tothe second slot 204 through some channels 222, and from the second slot204 back to the first slot 202 through other channels 222. Channels 222in which no pump actuator 216 b is active have little or no fluid flow.In this embodiment, fluid flowing through channels 222 to or from afluid slot also flows through fluid ejection chambers 210 of theinternal columns 220 a and 220 b.

FIG. 6 shows a top down view of a fluid ejection device 114, accordingto another embodiment of the disclosure. The FIG. 6 embodiment issimilar to the embodiments described in FIG. 4. Thus, the embodiment ofFIG. 6 includes a perimeter fluidic channel 400 disposed along bothsides and both ends of the substrate 200. The perimeter fluidic channel400 is fluidically coupled to fluid ejection chambers 210 and fluid pumpchambers 212 from the first external column 218 a and the secondexternal column 218 b. However, in this embodiment the internal columns220 of chambers have fluid ejection chambers 210 without any fluid pumpchambers 212. In this embodiment, instead of having fluid pump chambers212 taking up chamber locations in the internal columns 220 a and 220 b,that could otherwise be used for fluid ejection chambers 210, additionalchamber locations are formed further toward the center of the diesubstrate 200 within some of the channels 222 that provide for fluidpump chambers 212 and associated pump actuators 216 b. Fluid circulationpatterns are determined in this embodiment based on the channels 222 inwhich fluid pump chambers 212 (and pump actuators 216 b) are located,and based on where fluid pump chambers 212 are located in the externalcolumns 218. Thus, fluid circulation across the center of the diesubstrate 200 from slot-to-slot will occur through channels 222 havingfluid pump chambers 212 but not through channels 222 without fluid pumpchambers. Likewise, fluid circulation between slots 202 and 204 aroundthe perimeter fluidic channel 400 occurs through fluid pump chambers 212in the external columns 218. As in the previous embodiment, the fluidcirculation module 126 executing on controller 110 to control which pumpactuators 216 b are active and inactive determines which direction thefluid circulates between the slots through channels 222 and 400.

FIG. 7 shows a top down view of a fluid ejection device 114, accordingto an embodiment of the disclosure. The FIG. 7 embodiment is similar tothe embodiments described in FIG. 2. Thus, chambers in the externalcolumns 218 are fluid ejection chambers 210, while chambers in theinternal columns 220 a and 220 b are fluid pump chambers 212. However,in this embodiment one or more plenums 700 formed in the chamber layer206 and located toward the center of the die substrate 200. The plenums700 bring together a number of channels 222 from both the internalcolumns 220 a and 220 b. Thus, fluid being circulated from one slotthrough channels 222 by a number of fluid pump chambers 212 with activepump actuators 216 b flows into one side of a plenum 700. The fluidcirculates out of the other side of the plenum 700 through continuingchannels 222 and fluid pump chambers 212 with inactive pump actuators216 b before entering the other slot. While particular channel andplenum implementations or designs have been discussed and shown in thefigures, the concepts of slot-to-slot fluid circulation through channelsand plenums are not limited to these implementations. Rather, variousother channel and plenum implementations or designs are possible and arecontemplated herein as being appropriate for implementing slot-to-slotfluid circulation.

FIGS. 8-10 illustrate modes of operation for fluid pump actuators 216 bthat provide slot-to-slot fluid circulation through fluidic channels 222in a fluid ejection device 114. FIG. 8 shows a fluidic channel 222having closed fluid pump chambers 212 with fluid pump actuators 216 blocated toward each end of the channel, according to an embodiment ofthe disclosure. The ends of the fluidic channel 222 are in fluidcommunication with fluid slots 202 and 204. In general, an inertialpumping mechanism enables a pumping effect from a fluid pump actuator216 b in a fluidic channel 222 based on two factors. These factors arethe asymmetric (i.e., off-center, or eccentric) placement of theactuator 216 b in the channel 222 with respect to the length of thechannel, and the asymmetric operation of the actuator 216 b.

As shown in FIG. 8, each of the two fluid pump actuators 216 b islocated asymmetrically (i.e., off-center, or eccentrically) towardopposite ends in the channel 222. This asymmetric actuator placement,along with an asymmetric operation of the actuator 216 b (i.e., thegeneration of compressive and expansive/tensile fluid displacementshaving different durations) enables the inertial pumping mechanism ofthe actuator 216 b. The asymmetric location of the actuator 216 b withinthe channel 222 creates an inertial mechanism that drives fluidicdiodicity (net fluid flow) within the channel 222. A fluidicdisplacement from an active actuator 216 b generates a wave propagatingwithin the channel 222 that pushes fluid in two opposite directions. Themore massive part of the fluid contained in the longer side of thechannel 222 (i.e., away from the active actuator 216 b toward the farend of the channel 222) has larger mechanical inertia at the end of aforward fluid actuator pump stroke (i.e., deflection of the actuator 216b into the channel 222 causing a compressive fluidic displacement).Therefore, this larger body of fluid reverses direction more slowly thanthe fluid in the shorter side of the channel 222 (i.e., the short partof the channel 222 between the slot 202 and the active actuator 216 b).The fluid in the shorter side of the channel 222 has more time to pickup the mechanical momentum during the reverse fluid actuator pump stroke(i.e., deflection of the active actuator 216 b back to its initialresting state or further, causing an expansive fluidic displacement).Thus, at the end of the reverse stroke the fluid in the shorter side ofthe channel 222 has larger mechanical momentum than the fluid in thelonger side of the channel 222. As a result, the net fluidic flow movesin the direction from the shorter side of the channel 222 to the longerside of the channel 222, as indicated by the black direction arrow inFIG. 8. The net fluid flow is a consequence of the non-equal inertialproperties of two fluidic elements (i.e., the short and long sides ofthe channel 222).

Different types of actuator elements provide different levels of controlover their operation. For example, a thermal resistor actuator element216 b as shown in FIG. 8 provides fluid displacements during theformation and dissolution of vapor bubbles 800. The formation of a vaporbubble 800 causes a compressive fluid displacement, and the dissolutionof the vapor bubble causes an expansive or tensile fluid displacement.The durations of the compressive fluid displacement (i.e., the formationof the vapor bubble) and the expansive fluid displacement (i.e., thedissolution of the vapor bubble) are not controllable. However, thedurations of the displacements are asymmetric (i.e., the durations arenot the same lengths of time), which enables the thermal resistoractuator to function as a pump actuator 216 b when activated atappropriate intervals by controller 110.

FIG. 9 shows a fluidic channel 222 having closed fluid pump chambers 212with piezoelectric fluid pump actuators 216 b located toward each end ofthe channel, according to an embodiment of the disclosure. FIG. 9 alsoincludes a graph 900 showing a voltage waveform from a controller 110executing a fluid circulation module 126 to control the asymmetricoperation of a piezoelectric actuator 216 b in one embodiment. Apiezoelectric actuator element provides compressive fluid displacementswhen the piezoelectric membrane deflects into the channel 222, andexpansive/tensile fluid displacements when the piezoelectric membranereturns to its normal position or deflects out of the channel 222. Asthe graph 900 shows, the controller 110 is controlling the piezo pumpactuator 216 b near fluid slot 202 to generate compressive fluiddisplacements that are shorter in duration than the expansive/tensilefluid displacements. The result of the displacements from the activepiezo pump actuator 216 b located asymmetrically in the channel 222 is anet fluid flow through the channel 222 that circulates fluid from fluidslot 202 to fluid slot 204. Although not shown, if the same voltagecontrol waveform is applied to control the piezo pump actuator 216 bnear fluid slot 204, the direction of fluid flow through channel 222would reverse, causing fluid circulation from fluid slot 204 to fluidslot 202.

FIG. 10 shows a fluidic channel 222 having closed fluid pump chambers212 with piezoelectric fluid pump actuators 216 b located toward eachend of the channel, according to an embodiment of the disclosure. FIG.10 also includes a graph 1000 showing a voltage waveform from acontroller 110 executing a fluid circulation module 126 to control theasymmetric operation of a piezoelectric actuator 216 b in oneembodiment. In the embodiment of FIG. 10, the controller 110 iscontrolling the piezo pump actuator 216 b near fluid slot 202 togenerate compressive fluid displacements that are longer in durationthan the expansive/tensile fluid displacements. The result of thedisplacements from the active piezo pump actuator 216 b locatedasymmetrically in the channel 222 is a net fluid flow through thechannel 222 that circulates fluid from fluid slot 204 to fluid slot 202.Although not shown, if the same voltage control waveform is applied tocontrol the piezo pump actuator 216 b near fluid slot 204, the directionof fluid flow through channel 222 would reverse, causing fluidcirculation from fluid slot 204 to fluid slot 202.

FIG. 11 shows a flowchart of an example method 1100 of circulating fluidfrom slot-to-slot in a fluid ejection device 114, according to anembodiment of the disclosure. Method 1100 is associated with theembodiments discussed herein with respect to FIGS. 1-10.

Method 1100 begins at block 1102 with pumping fluid over a central areaof a die substrate from a first slot to a second slot through a firstfluidic channel, where the first fluidic channel extends from the firstslot through a first chamber adjacent the first slot, across the centralarea, and to the second slot through a second chamber adjacent thesecond slot. As shown at block 1104 of method 1100, pumping fluid fromthe first slot to the second slot can include generating compressive andexpansive fluid displacements of different durations from a firstactuator in the first chamber while generating no fluid displacementsfrom a second actuator in the second chamber. Pumping fluid from thefirst slot to the second slot can additionally include pumping fluidfrom the first slot with a plurality of active pump actuators through aplurality of fluidic channels into a plenum, as shown at block 1106, andpumping fluid from the plenum through a plurality of fluidic channelsinto the second slot, as shown at block 1108.

Method 1100 continues at block 1110, with pumping fluid over the centralarea from the second slot to the first slot through a second fluidicchannel, where the second fluidic channel extends from the second slotthrough a third chamber adjacent the second slot, across the centralarea, and to the first slot through a fourth chamber adjacent the firstslot. As shown at block 1112 of method 1100, pumping fluid from thesecond slot to the first slot can include generating compressive andexpansive fluid displacements of different durations from a thirdactuator in the third chamber while generating no fluid displacementsfrom a fourth actuator in the fourth chamber. Pumping fluid from thesecond slot to the first slot can additionally include pumping fluidfrom the second slot with a plurality of active pump actuators through aplurality of fluidic channels into a plenum, as shown at block 1114, andpumping fluid from the plenum through a plurality of fluidic channelsinto the first slot, as shown at block 1116.

The method 1100 continues at block 1118, with pumping fluid around aperimeter of the die substrate through a perimeter fluidic channel thatencircles the first and second slots.

What is claimed is:
 1. A fluid ejection device comprising: a dischargeport; an energy generating element to discharge liquid through thedischarge port; a first liquid supply on a first side of the dischargeport; a second liquid supply on a second side of the discharge portopposite the first side; a first liquid flow path extending from thefirst liquid supply to the discharge port; a second liquid flow pathextending from the second liquid supply to the discharge port; a fluiddisplacement actuator in the first liquid flow path; and a second fluiddisplacement actuator in the first liquid flow path between the firstliquid supply and the discharge port.
 2. The fluid ejection device ofclaim 1, wherein the fluid displacement actuator is asymmetricallypositioned within the first liquid flow path with respect to firstliquid supply and the discharge port.
 3. The fluid ejection device ofclaim 1, wherein the first liquid flow path linearly extends from thefirst fluid supplied to the discharge port, wherein the second fluiddisplacement actuator is between the first fluid displacement actuatorand the discharge port.
 4. The fluid ejection device of claim 1 furthercomprising: a second discharge port; a second energy generating elementto discharge liquid through the second discharge port; a third liquidflow path on a first side of the second discharge port, the third liquidflow path extending parallel to the first liquid flow path; a fourthliquid flow path on a second side of the second discharge port oppositethe first side of the second discharge port, the fourth liquid flow pathextending parallel to the second liquid flow path; and a third fluiddisplacement actuator in the third liquid flow path.
 5. The fluidejection device of claim 4, wherein the third fluid displacementactuator is asymmetrically positioned within the third liquid flow path.6. The fluid ejection device of claim 5 further comprising a fourthfluid displacement actuator in the second liquid flow path between thethird fluid displacement actuator and the second discharge port.
 7. Thefluid ejection device of claim 6, wherein the third liquid flow path islinear.
 8. The fluid ejection device of claim 4 further comprising: athird discharge port; a third energy generating element to dischargeliquid through the third discharge port; a fifth liquid flow path on afirst side of the third discharge port, the fifth liquid flow pathextending parallel to the first liquid flow path; a sixth liquid flowpath on a second side of the third discharge port opposite the firstside of the third discharge port, the sixth liquid flow path extendingparallel to the second liquid flow path; and a fourth fluid displacementactuator in the fourth liquid flow path.
 9. The fluid ejection device ofclaim 8, wherein the first discharge port, the second discharge port andthe third discharge port are in a column of ports and wherein the firstliquid flow path, the third liquid flow path and the fifth liquid flowpath have respective mouths in a column of mouths parallel to the columnof ports.
 10. The fluid ejection device of claim 1, wherein the firstliquid supply comprises a first slot and wherein the second liquidsupply comprises a second slot parallel to the first slot.
 11. The fluidejection device of claim 1, wherein the fluid displacement actuatorcomprises a thermal resistor element.
 12. A fluid ejection devicecomprising: a column of discharge ports; a column of energy generatingelements to discharge liquid through respective ports of the column ofdischarge ports; a first series of parallel liquid flow paths extendingfrom inlet ports of a column of inlet ports to respective ports of thecolumn of discharge ports; a second series of parallel liquid flow pathsopposite the first series of parallel liquid flow pass, the secondseries of parallel liquid flow paths extending to respective ports ofthe column of discharge ports; a fluid displacement actuator in eachflow path of the first series of parallel liquid flow paths; and asecond fluid displacement actuator in each flow path of the first seriesof parallel liquid flow paths.
 13. The fluid ejection device of claim12, wherein the fluid displacement actuator is asymmetrically positionedbetween a respective one of the inlet ports and the respective dischargeport.
 14. The fluid ejection device of claim 12 further comprising: afirst slot connected to each of the inlet ports; and a second slotconnected to each of the liquid flow paths of the second series ofparallel liquid flow paths.
 15. The fluid ejection device of claim 12,wherein the fluid displacement actuator comprises a thermal resistorelement.
 16. The fluid ejection device of claim 12, wherein each liquidflow path of the first series of liquid flow paths linearly extends tothe respective discharge port, wherein the second fluid displacementactuator is between the respective fluid displacement actuator and therespective discharge port.
 17. The fluid ejection device of claim 16,wherein the fluid displacement actuator is asymmetrically positionedbetween the respective inlet port and the respective discharge port andwherein the second fluid displacement actuator is asymmetricallypositioned between the respective inlet port and the respectivedischarge port.
 18. The fluid ejection device of claim 12, wherein eachof the second series of parallel liquid flow past extends from arespective outlet port of a column of outlet ports.
 19. A fluid ejectiondevice comprising: a discharge port; an energy generating element todischarge liquid through the discharge port; a first liquid supply on afirst side of the discharge port; a second liquid supply on a secondside of the discharge port opposite the first side; a first liquid flowpath extending from the first liquid supply to the discharge port; asecond liquid flow path extending from the second liquid supply to thedischarge port; a fluid displacement actuator in the first liquid flowpath; a second discharge port; a second energy generating element todischarge liquid through the second discharge port; a third liquid flowpath on a first side of the second discharge port, the third liquid flowpath extending parallel to the first liquid flow path; a fourth liquidflow path on a second side of the second discharge port opposite thefirst side of the second discharge port, the fourth liquid flow pathextending parallel to the second liquid flow path; and a second fluiddisplacement actuator in the third liquid flow path.
 20. The fluidejection device of claim 19, wherein the third second fluid displacementactuator is asymmetrically positioned within the third liquid flow path.